Arc heater apparatus



Jan. 3, 1967 F, B. JOHNSON 3,296,479

ARC HEATER APPARATUS Filed May 21, 1963 WITNESSES: INVENTOR y Frederick B Johnson fi fir? e-ma aw 3,296,479 ARC HEATER APPARATUS Frederick B. Johnson, Pleasant Hills, Pa, assignor to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed May 21, 1963, Ser. No. 282,073 Claims. (Cl. 313-446) The present invention relates to apparatus for increasing the enthalpy of a gas, and more particularly to are heater apparatus for providing a gas at very high temperatures and velocities.

A typical arc heater used for increasing the enthalpy of a gas has a plurality of electrodes contained within a chamber. An arc is established between the electrodes and the process gas is caused to move through the chamber. The gas on being exposed to the heat of the arc absorbs heat thereby increasing its temperature and enthalpy. The gas is then discharged from the chamber in this condition. Apparatus of this type for producing hot gases finds many applications especially in laboratory investigations, materials research, thermodynamic studies, chemical synthesis studies, metal processing and various other high temperature and velocity testing applications.

Among the problems encountered in air are heating apparatus is that of initiating the arc. One way of doing this is to utilize a starting fuse between the electrodes. Vaporization of the fuse creates an ionized path through the normally high dielectric strength material between the electrodes. The difficulty of access to the inside of the chamber of the heater apparatus limits the feasibility of the fuse method for short run operation. Another method is to utilize one movable electrode which first touches the other electrode, thus establishing a power circuit. An arc is then drawn in the space between electrodes as the movable electrode returns to its operating position. Previously this method has given rise to complex mechanical arrangements and has encountered problems of leakage around the movable electrode.

Another serious problem is the possible non-uniform heating of the process gas, since in many of the prior designs the gas passed through the are once or only a few times before being expelled from the chamber. The non-uniform heating of the gas has serious deleterious effects especially in chemical synthesizing and metal processing applications.

It is therefore an object of the present invention to provide new and improved arc heating apparatus which affords easy start up operation.

It is a further object of the present invention to provide new and improved arc heating apparatus for supplying process gas which is uniformly heated.

It is a further object of the present invention to provide new and improved arc heating apparatus which eliminates the aforementioned problems while providing a relatively simple and efficient structure.

Generally stated, the above cited objects are accomplished in arc heater apparatus, wherein gas is heated in a chamber defined by a substantially cylindrical electrode. A movable electrode is disposed in the chamher and may be tilted to contact the cylindrical electrode to establish an arc between the electrodes. A magnetic field applied substantially transverse to the arc imparts a rotational motion to the arc. The gas introduced into the chamber is thus heated by the rotating arc and then expelled from the chamber.

More specifically, the movable electrode may be circular or disc-like in shape. In the operating position this electrode is inside and concentric to the outside cylindrical electrode. A magnetic field is provided across the space between the electrodes, this field being oriented United States Patent 1 O Patented Jan. 3, 1967 ice perpendicular to the direction of current flow in the are between the electrodes. The are column is essentially a conductor between the electrodes and moves rotationally, under the influence of the magnetic field, in the circular space between the electrodes in much the same manner as the armature of an electric motor. The process gas is then caused to move slowly longitudinally through the chamber and in so doing it moves through the space between the two electrodes. By making the gas movement slow with respect to speed of rotation of the arc each element of the gas is intimately exposed to the heat of the are a number of times before'it reaches the discharge section of the chamber. This results in uniform heating of all elements of the gas before discharge from the chamber.

These and other objects will become more apparent when considered in view of the following specification and drawing, in which, the single figure is a sectional view of the air are heater apparatus of the present invention.

Referring now to the single figure, the left half of the are air heater apparatus is shown in cross section, the apparatus being symmetrical about the center longitudinal axis II. The outside case wall includes three basic components: the electrode member 2, the insulating tubes 4 and 6 and the end pressure plates 8 and 10. The power electrode member 2 is one of the main power electrodes. This electrode includes a cylindrical block of electrically conducting metal comprising copper or zirconium copper, for example. The inside surface of the electrode 2 adjacent the arcing area 12 is lined with a copper tube 13, which is circumferentially wound on the surface and is brazed to the surface of the electrode 2. The tube 13 has a passage therethrough through which water or other fluid may be passed to cool the surface of the electrode 2. In cross section, the surface of the electrode 2 including the tubing 13 is in an S shape as shown. The tube 13 itself thus becomes the part of the electrode exposed to the arcing area 12. The inlet source for the cooling water to be supplied to the tube 13 is not shown for simplicity. A terminal 15 is connected through an electrical conductor to the electrode member 2 so that an electrical potential may be applied to this electrode as discussed below. Placed at each end of the central electrode member 2 are the cylindrical tubes 4 and 6, which comprise a high strength electrical and temperature insulating material, such as glass epoxy.

The outside casing wall is closed by the end pressure plates 8 and 10 disposed, respectively, at the top and bottom of the apparatus. These end plates comprise steel plates of sufficient strength to stand the internal design pressure within the chamber. The case wall members 2, 4, 6, 8 and 10 are held together by a plurality of studs 14, which may comprise stainless steel. The studs are wrapped their full length with thermalastic or similar insulation to provide electrical insulation between the end plates 8 and 10 and the central electrode 2. To provide a gas tight seal between the various members of the case assembly an O-ring gasket 16 is disposed between the central electrode 2 and the insulating tube 4, an O-ring gasket 18 is disposed between the central electrode 2 and the insulating tube 6, an O-ring gasket 20 is disposed between the end pressure plate 8 and the insulating tube 4, and O-ring gasket 22 is disposed between the end plate 10 and the insulating tube 6. The nuts 24 and 26 are affixed to the stud 14 in order to maintain the apparatus in a gas-tight relationship.

The bottom or upstream pressure plate 10 has one or more apertures 28 drilled therein so that input gas ca be introduced into the chamber to be heated.

A disc-shaped inner power electrode 30 is disposed within the arc chamber adjacent the arcing area 12. This inner electrode 30 is disposed along the axis I--I so that it is concentric with the outer electrode 2. The disc electrode 30 comprises an electrically conductive material, such as copper. Wound on the outer surface of the electrode 36 is a copper tube 32, which is brazed to the outer surface of the electrode 30. Two concentric electrically conducting pipes 34 and 36 support the disc electrode 30 in position. The electrode 30 is rigidly attached to these concentric pipes 34 and 36, which comprise an electrically conductive material such as copper. The concentric pipes 34 and 36 extend through the bottom base plate 10 through a clearance hole therein. Cooling water or other fluid is supplied to the tube 32 attached to the electrode 30 through the spaces 38 and 40 which are formed within the pipe 36 and between the concentric pipes. Water or other liquid may, for example, be introduced through the opening '38 and dispelled through the opening 40. The coolant introduced into the tube 32 serves to cool the electrode 30. The outer pipe 34 is wound over a considerable portion with an electrically insulating layer 39 comprising a thermoplastic tapeor similar insulation to insulate the electrode 30 from the pressure plate 10. The disc electrode member 30 with the tube 32 surface and the concentric pipes 36 and 38 are herein designated the electrode assembly.

Electrically connected to the concentric tubes 34 and 36 is the terminal 42. An electrical potential of suitable magnitude is applied across the terminals 42 and 15, which is connected to the outer electrode 2. The mag nitude of this potential is so selected that under normal operating conditions it will maintain an arc between the electrodes 2 and 30. The potential may either be alternating or direct so long as it will establish and maintain an arc.

The entire inner electrode assembly is attached to the bottom plate 10 through the mounting flange 44. The mounting flange 44 includes the trunnion bearing 46, which allows the electrode assembly to be tilted toward the outer electrode 2 so that the outer surface tube 13 of the electrode 2 may come in contact with the tube 32 of the inner electrode 30. The movability of the inner electrode permits an arc to be started readily between the electrodes 2 and 30. The flange member 44 including the trunnion bearing 46 is rigidly fixed to the end plate through the bolts 48 and 50.

A boot shaped member 52 of an electrically insulating material comprising silicone rubber, for example, is fitted around the inner electrode assembly, being secured by the flange 54 to the pipe 34 and to the pressure plate 10 by the flange 56. The boot member 52 is so situated to prevent gas leakage between the electrode assembly and the pressure plate 10. An electrically insulating disc-shaped member 58 is mounted around the pipe 34 and fixed thereto by the flange assembly 54. This insulating disc may, for example, comprise a high temperature insulating material, such as porous zirconia or porous alumina. The function of the disc 58 is to shield the insulating member 6 and the boot member 52 from the radiant heat produced by the are within the arcing area 12. The disc 58 also effects a reasonably uniform flow of process gas through the heater apparatus.

A nozzle member 60 extends through an aperture in the top pressure plate 8 and extends down into the chamber to be adjacent the arcing area 12. The surface of the nozzle 60 adjacent the hot gas in the arcing area is cooled by providing the manifold 62 extending around the inner :surface of the nozzle. Cooling water or other fluid may then be passed through the manifold 62 to cool the surface of the nozzle from external means (not shown). The nozzle 60 may comprise such materials as copper, zirconium copper or silver, for example, with the surface 64 of the nozzle also comprising a similar material.

A field coil 66 is disposed about and insulated from ,the cylindrical outer electrode member 2. The field coil 66 is energized by a source of alternating or direct current through the terminals 68 and 70. The coil 66 is so wound to provide a magnetic field B substantially in the longitudinal axial direction I-I of the chamber. The magnetic field B is then substantially transverse to any radial are drawn between the electrodes 2 and 30. The radial are drawn between the electrodes will. be rotated under the presence of the magnetic field, the interacting of the current density between theelectrodes and the magnetic field to produce a force on the arc. The rotation of the arc will aid in allowing the electrodes to have long life as the rotation of the arc will tend to limit localized heating of the electrode surfaces at any one spot. The rotating arc comes into contact with the gas introduced into the chamber through the aperture 28 and this gas is heated on passing through the arc. The heated gas is then expelled through the nozzle 60 at high temperatures. Because the cross section of the annular space between the electrodes 2 and 36 is large compared to the opening in thenozzle the movement of the gas through the arcing area is relatively slow thus permitting the gas to be adequately heated. With the proper selection of arcing potential applied between the terminals 15 and 42 and the proper selection of the excitation current applied to the terminals 68 and 70 of the field coil 66, the radial are between the electrodes will rotate at a relatively high speed so that each increment of gas when passing through the arcing area 12 will be subjected to the heating etfect' of the are several times. Therefore, because of the relatively slow movement of the gas and the relatively high rotational speed of the are each increment of gas will tend to be uniformly heated which is quite advantageous in many processes. On being expelled through the nozzle 60 the gas may be utilized for any of the applications as discussed above by the suitable connection of testing or utilization apparatus to the outer surface of the nozzle member 60.

At start-up, an arc may easily be drawn by tilting the inner electrode assembly from the outside by for example applying an external force to the pipe members 34 and 36 to cause the electrode 30 to come in contact with the outer electrode 2. To vary the length of arc between the electrodes several different inner electrode assemblies may be inserted intothe chamber to increase or lengthen the are drawn between the outer and inner electrodes. Moreover, the electrode assembly may readily be taken from the case assembly for inspection or to repair any or replace any of the components.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of structure and combination and arrangement ofparts may be resorted to without departing from the scope and the spirit of the present invention.

I claim as my invention:

1. In arc heater apparatus for increasing the enthalpy of a gas, the combination of: a chamber including a cylindrical electrode, a first pressure plate and a secondpressure plate, the second pressure plate having an opening therein; a movable electrode having a disc-shaped portion forming an arcing surface and extending into said ch-amher through the opening in the second pressure plate,- the plane of the disc-shaped portion of the movable electrode being normally positioned substantially perpendicular to the longitudinal axis of the cylindrical electrode whereby an annular arc gap is formed between the outer periphery of the disc-shaped portion of the movable electrode and the inner Wall of said cylindrical electrode; mounting means including a trunnion bearing securing the movable electrode to the second pressure plate whereby the movable electrode may be titled to bring the disc-shaped portion thereof into contactwith the cylindrical electrode; supply means to apply a source of potential to said electrodes of sufiicient magnitude to sustain an arc therebetween, the contact between the movable elect-rode and the circular inner wall of the cylindrical electrode starting the arc whereafter the movable electrode is moved back to its normal position; inlet means for admitting a flow of gas into said chamber to be heated; magnetic means to provide a magnetic field substantially transverse to the are drawn between said electrodes; and exhaust means extending into said chamber for discharging the heated gas from said chamber.

2. In arc heater apparatus for increasing the enthalpy of a gas, the combination of: a chamber including an outer electrode member having a substantially cylindrical shape, a top pressure plate and a bottom pressure plate disposed at the ends of said outer electrode member; a movable disc-shaped inner electrode member having an elongated support portion extending through said bottom pressure plate into said chamber whereby an annular arc gap is formed between the outer periphery of the discshaped electrode member and the cylindrical wall of the outer electrode member while the inner disc-shaped electrode member is in its normal position; means tiltably mounting the movable electrode on the bottom pressure plate; supply means to .apply a source of potential to said inner and outer electrode members of sufficient magnitude to sustain an arc therebetween, said inner electrode member when tilted coming into contact with the cylindrical wall of said outer electrode member initiating an arc therebetween and being thereafter movble to its normal position; inlet means for admitting a flow of gas into said chamber to be heated; magnetic means to provide a magnetic field substantially transverse to the are drawn between said electrode members, and exhaust means including a nozzle extending into said chamber for discharging the heated gas from said chamber.

3. In are heater apparatus for increasing the enthalpy of a gas, the combination of: a chamber including a cylindrical electrode member, a top pressure plate and a bottom pressure plate; electrode means including a movable electrode member disposed through said bottom pressure plate into said chamber and including means tiltably mounting the last-named electrode member in the bottom press-ure'plate, the axis of the movable electrode member normally substantially coinciding with the longitudinal axis of the cylindrical electrode member, a radially extending annular arc gap being formed between said electrode members; a boot-shaped member composed of resilient electrically insulating material disposed around the portion of the movable electrode member adjacent the mounting means and preventing gas leakage from the chamber; supply means to apply a source of potential to said electrode members of sufiicient magnitude to sustain an arc therebetween, the movable electrode member upon tilting making contact with the cylindrical electrode member to start the arc and being thereafter moved to its normal position; inlet means for admitting a flow of gas into said chamber to be heated; magnetic means disposed about said chamber to provide a magnetic field substantialy transverse to the are drawn between said electrode members; and exhaust means including a nozzle dis-posed through said top pressure plate into said chamber for discharging the heated gas firomsaid chamber.

4. In arc heater apparatus for increasing the enthalpy of a gas, the combination of: a chamber including an outer electrode member having a substantially cylidrical shape, a top pressure plate and a bottom pressure plate disposed over the respective ends of said outer electrode member; electrode means including an inner movable disc-shaped electrode member disposed through said bottom pressure plate into said chamber and including means tiltably mounting the last-named electrode member in the bottom pressure plate, said inner electrode member being tiltable to come in contact with said outer electrode member to start the arc and thereafter being movable to its normal position, a radially extending annular arc gap being formed between said electrode members while the movable electrode member is in its normal position; supply means to apply a source of potential to said electrode members of sufiicient magnitude to sustain an arc between said electrode members; inlet means for admitting a flow of gas into said chamber to be heated; a boot-shaped composed of resilient electrically insulating material disposed around the portion of the movable electrode member adjacent the mounting means and preventing gas leakage from the chamber; disc-like shield means adjacent the inner end of the boot-shaped member and shielding the boot-shaped member from radiation from the arc; magnetic means disposed about said chamber to provide a magnetic field substantially transverse to the are drawn between said electrode members; and exhaust means disposed through said top pressure plate into said chamber for discharging the heated gas from said chamber.

5. In arc heater apparatus for increasing the enthalpy of a gas, the combination of: a chamber including an outer fluid cooled electrode member having a substantially cylindrical shape, a top pressure plate and a bottom pressure plate disposed over the ends of said outer electrode member, the bottom pressure plate having an opening therein; a fluid cooled movable disc-shaped inner electrode member extending through the opening in said bottom pressure plate into said chamber whereby a radially exending annular arc gap is formed between said electrode members while the movable electrode member is in its normal position; mounting means including a trunnion bearing securing the movable electrode member to the bottom pressure plate whereby the movable electrode member may be tilted to bring the disc shaped portion thereof into contact with the outer electrode; supply means to apply a source of potential to said electrode members of sufficient magnitude to sustain an arc therebetween, the movable disc-shaped electrode member being tilted into contact with the cylindrical outer electrode member to start the arc and being thereafter moved to its normal position; inlet means for admitting a flow of gas into said chamber to be heated; a boot-shaped member composed of resilient electrically insulating material disposed around the portion of the movable electrode member adjacent the mounting means and preventing gas leakage from the chamber; disc-like shield means adjacent the inner end of the boot-shaped member and shielding the boot-shaped member from radiation from the arc; magnetic means disposed about said chamber to provide a magnetic field in the axial direction of said outer electrode member; and exhaust means including a fluid cooled nozzle disposed through said top pressure plate into said chamber for discharging the heated gas from said chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,545,345 3/1951 Deri 313-152 3,048,736 8/ 1962 Emmerich 3 l51 11 3,097,321 7/ 1963 Row 313 146 3,182,176 5/1965 Bunt et a1. 313-231 DAVID I. GALVIN, Primary Examiner. 

1. IN ARC HEATER APPARATUS FOR INCREASING THE ENTHALPY OF A GAS, THE COMBINATION OF: A CHAMBER INCLUDING A CYLINDRICAL ELECTRODE, A FIRST PRESSURE PLATE AND A SECOND PRESSURE PLATE, THE SECOND PRESSURE PLATE HAVING AN OPENING THEREIN; A MOVABLE ELECTRODE HAVING A DISC-SHAPED PORTION FORMING AN ARCING SURFACE AND EXTENDING INTO SAID CHAMBER THROUGH THE OPENING IN THE SECOND PRESSURE PLATE, THE PLANE OF THE DISC-SHAPED PORTION OF THE MOVABLE ELECTRODE BEING NORMALLY POSITIONED SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINAL AXIS OF THE CYLINDRICAL ELECTRODE WHEREBY AN ANNULAR ARC GAP IS FORMED BETWEEN THE OUTER PERIPHERY OF THE DISC-SHAPED PORTION OF THE MOVABLE ELECTRODE AND THE INNER WALL OF SAID CYLINDRICAL ELECTRODE; MOUNTING MEANS INCLUDING A TRUNNION BEARING SECURING THE MOVABLE ELECTRODE TO THE SECOND PRESSURE PLATE WHEREBY THE MOVABLE ELECTRODE MAY BE TITLED TO BRING THE DISC-SHAPED PORTION THEREOF INTO CONTACT WITH THE CYLINDRICAL ELECTRODE; SUPPLY MEANS TO APPLY A SOURCE OF POTENTIAL TO SAID ELECTRODES OF SUFFICIENT MAGNITUDE TO SUSTAIN AN ARC THEREBETWEEN, THE CONTACT BETWEEN THE MOVABLE ELECTRODE AND THE CIRCULAR INNER WALL OF THE CYLINDRICAL ELECTRODE STARTING THE ARC WHEREAFTER THE MOVABLE ELECTRODE IS MOVED BACK TO ITS NORMAL POSITION; INLET MEANS FOR ADMITTING A FLOW OF GAS INTO SAID CHAMBER TO BE HEATED; MAGNETIC MEANS TO PROVIDE A MAGNETIC FIELD SUBSTANTIALLY TRANSVERSE TO THE ARC DRAWN BETWEEN SAID ELECTRODES; AND EXHAUST MEANS EXTENDING INTO SAID CHAMBER FOR DISCHARGING THE HEATED GAS FROM SAID CHAMBER. 